Parallel evolution of novelties: extremely long intromittent organs in the leaf beetle subfamily Criocerinae

The development of extremely large male genitalia under spatial limitation

Extensive research in evolutionary biology has focused on the exaggeration of sexual traits; however, the developmental basis of exaggerated sexual traits has only been determined in a few cases. The evolution of exaggerated sexual traits may involve the relaxation of constraints or developmental processes mitigating constraints. Ground beetles in the subgenus Ohomopterus (genus Carabus) have species-specific genitalia that show coevolutionary divergence between the sexes. Here, we examined the morphogenesis of the remarkably enlarged male and female genitalia of Carabus uenoi by X-ray microcomputed tomography. The morphogenetic processes generating the male and female genitalia at the pupal stage were qualitatively similar to those in closely related species with standard genital sizes. Higher growth rates contributed to the exaggeration of both the male and female genital parts of C. uenoi, possibly related to a gene network commonly upregulated in both sexes. Additionally, the length of the copulatory piece (CP), the enlarged male genital part stored in the aedeagus (AD), reached close to that of the AD at the later developmental stages and thereafter decelerated to grow in parallel with the AD, suggesting a structural constraint on the CP by the outer AD. Then, unlike related species, the lengths of the CP and AD increased at eclosion, suggesting a mechanism leading to further elongation of the male genitalia. These observations suggest that a developmental process allows continuous growth of the male genitalia even under the spatial limitation. These results revealed the spatio-temporal dynamics of the development of exaggerated genital structures under structural constraints.

Three new species and five new records within the genus Lilioceris (Coleoptera, Chrysomelidae, Criocerinae) from China

The Chinese species of Lilioceris are revised, and three new species are described from Tibet, China: Lilioceriszhentangensis Xu & Liang, sp. nov., Liliocerismedogensis Xu & Liang, sp. nov. and Lilioceriszayuensis Xu & Liang, sp. nov. Five species of Lilioceris are reported for China as new records: L.dromedarius (Baly, 1861), L.pulchella (Baly, 1859), L.semicostata (Jacoby, 1908), L.unicolor (Hope, 1831) and L.nepalensis Takizawa, 1989. Liliocerisseminigra (Jacoby, 1889) is proposed as a junior synonym of L.unicolor Hope, 1831. Redescriptions, habitus photographs, geographic distributions, host plants (if available) and habitats are provided for these species.

A review of the sinica species group within the genus Lilioceris (Coleoptera, Chrysomelidae, Criocerinae)

A new species group of the genus Lilioceris Reitter, 1913 is proposed and reviewed, the sinica group. It includes six species: L.gressitti Medvedev, 1958; L.rugata (Baly, 1865); L.sieversi (Heyden, 1887); L.sinica (Heyden, 1887); L.theana (Reitter, 1898) stat. nov.; and L.thibetana (Pic, 1916). Among them, L.theana is resurrected as a valid species from synonymy with L.rugata, and is newly reported from China. Redescriptions, an identification key, figures of habitus and male and female genitalia, geographic distributions, host plants, and habitats (if known) are provided for these species.

New record of the genus Manipuria Jacoby (Chrysomelidae, Criocerinae) from China, with description of a new species

After a century since the erection of the genus Manipuria from India, its type species M.dohertyi Jacoby was discovered in Yunnan Province of China. A new Manipuria species, M.yuaesp. nov., is described from Tibet and Yunnan, China. The new species differs from M.dohertyi by its larger size, unicolored elytra, and absence of a tooth-like prolongation in front of the mandible. Additional data is provided for M.dohertyi based on new material from China.

Sperm transfer through hyper-elongated beetle penises - morphology and theoretical approaches

Many insects possess a hyper-elongated intromittent organ with a diameter of only a few micrometers. Using morphological and theoretical approaches, we investigated the biomechanics of sperm transfer through such organs by calculating (1) how far and how fast sperm could fill in the penis by capillary action, (2) how much capillary pressure is generated in the penis, and (3) how much pressure is needed to pump sperm out of the penis. The results enabled us to propose the following hypotheses: (1) penile filling basically occurs by capillary action, and (2) sperm transport to females occurs by contracting the sperm pump muscles or by active propulsion of spermatozoa. Potential experimental approaches to test these hypotheses are discussed.

Eversion and withdrawal of an intromittent organ before sexual maturation prepares male beetles for copulation

Some species of criocerine beetles have a hyper-elongated part of the intromittent organ called a flagellum. In resting position, the flagellum is stored in a specialized internal sac in the intromittent organ. This specialized state of the flagellum and internal sac is indispensable during copulation for flagellar insertion into the female spermathecal duct for sperm transfer. However, the morphogenesis of the flagellum does not generate the active state of the flagellum; rather, the flagellum is generated in an inactive and completely coiled state. After eclosion, males of Lema coronata evert and withdraw the internal sac multiple times before sexual maturation, without mounting a female. This behaviour serves to uncoil the flagellum and guide it into the active state with the aid of surface structures on the internal sac. A closely related species, Lema dilecta, also has a long flagellum and undergoes the same behaviour to place the flagellum in the active position. However, some other species of criocerine beetles with much shorter flagella can attain the active state without exhibiting this behaviour. Based on a previously proposed phylogenetic tree, we discuss the evolutionary history of the hyper-elongation of the flagellum and associated behaviour.

Evolution of a giant intromittent organ in Scydmaeninae (Coleoptera: Staphylinidae): functional morphology of the male postabdomen in Mastigini

We compared the postabdominal architecture of Mastigini with extremely long (Stenomastigus) or short (Palaeostigus) aedeagus. A novel mode of copulation was discovered: males of Stenomastigus insert a paramere between the female's abdomen and elytra, and the intromission is stabilized by several structures of both sexes. The intrinsic aedeagal mechanism is indicated as responsible for inflating the endophallus, and the long flagellum does not penetrate the ductus spermathecae during copulation. The structure of the flagellum suggests that it is primarily responsible for the sperm transfer. Asymmetrical postabdominal rotators of the aedeagus were only found in Stenomastigus; they presumably facilitate the withdrawal of the genitalia; their origin as bundles separated from larger muscles is postulated. We discuss a scenario in which the evolution of elongated genitalia was facilitated by the lack of structural constraints and existing preadaptations. Benefits of stabilizing the copulation and intromission are indicated as the driving force for the evolution of extremely long aedeagi, while the short aedeagi might have the advantage of freedom of movements facilitating the initiation of copulation by males. Disruptive selection is suggested as a working hypothesis to further investigate mechanisms that have played a role in the evolution of genital structures of Mastigini.